Relationship of duration of androgen blockade and response to antiandrogen withdrawal: A retrospective study.

e15104 Background: Patients with progressive prostate cancer treated with androgen blockade, might achieve prostate-specific antigen (PSA) decline or stabilization after discontinuation of antiandrogen treatment. This phenomenon is called antiandrogen withdrawal response and is often associated with clinical improvement. Methods: PSA response of 170 patients from two different centers was retrospectively analyzed. Eligible patients had progressive prostate cancer during treatment with androgen blockade (orchiectomy or LHRH agonist plus antiandrogen). Patients were stratified according to Gleason grade (≤6 vs >6), stage at diagnosis (II, III, IV), type of antiandrogen (bicalutamide, flutamide or steroidal antiandrogens) and duration of treatment blockade (≤12 or >12 months). Clinical benefit (CB) was defined as a confirmed PSA decline ≥50% or stabilization for ≥3 months. Results: Median age was 71 years (range 48 - 91). One hundred forty-one patients had a Karnofsky performance status (K PS) ≥ 80%. Of the 170 patients, 108 (63.5%) had PSA progression after antiandrogen withdrawal and 62 (36.5%) had PSA stabilization or decline. No significant correlation between stage, Gleason grade or K PS and CB was found. Ninety-eight (57.6%) patients had previously received bicalutamide, 52 (30.6%) flutamide and 20 (11.8%) steroidal antiandrogens. CB after antiandrogen withdrawal was observed in 37.8% (37/98), 44.2% (23/52) and 10% (2/20) of patients in the group of bicalutamide, flutamide and steroidal antiandrogens respectively (p=0.024). Longer duration of antiandrogen blockade was associated with CB: 40.5% (53/131) of patients who had received more than 12 months of antiandrogen blockade vs 23.1% (9/39) among patients who had received ≤ 12 months (p=0.0478). Median duration of response was 7 months (range 3 – 52). Conclusions: In patients with progressive prostate cancer, antiandrogen withdrawal may be a useful maneuver resulting, in some cases, in prolonged responses. According to this study, duration of androgen blockade treatment and use of non steroidal antiandrogen may predict a favorable response to antiandrogen withdrawal.